1. Field of the Invention
The present invention relates to a method for producing chemically and color stable cupric hydroxide compositions, suitable for use as a fungicide. In particular, the method employs a class of carbonate compounds as intermediates and may be characterized as carbonate process cupric hydroxide and is an improvement on similar types of processes by providing for control of particle size and bulk density of the resultant product.
2. Related Art
Cupric hydroxide, depending to a large extent on its method of production may not be a stable material. For example, when a base such as sodium hydroxide, is added to a solution of water soluble copper salts, e.g., copper sulfate, a blue, gelatinous precipitate is formed that gradually turns black in color. This material is unstable and contains cupric oxide hydrate and cupric oxide in addition to cupric hydroxide.
U.S. Pat. No. Re 24,324 disclosed a method for the preparation of stable cupric hydroxide. This procedure comprised reacting substantially equal molar amounts of copper sulfate and trisodium phosphate, to obtain a copper containing precipitate. The precipitate is then treated with sodium hydroxide in an amount sufficient to convert a major portion of the precipitate to cupric hydroxide. The sodium hydroxide regenerates the trisodium phosphate. The process is continued by alternately adding copper sulfate and sodium hydroxide. The trisodium phosphate is an intermediate and the alternating additions may be repeated 15 to 20 times in this manner. A solid product is obtained by separating solids, washing and drying the precipitate.
Other methods of preparing phosphate-process cupric hydroxide are disclosed in U.S. Pat. Nos. 2,924,505 and 3,628,920.
A particularly effective fungicidal and bactericidal copper material is disclosed in U.S. Pat. No. 3,428,731 wherein a stable dispersion of phosphate-process cupric hydroxide is obtained in an aqueous medium by having a pH in the range of about 7 to 9.5. This phosphate stabilized cupric hydroxide is suitable for use as a fungicide because of its fine particle size and high surface area, but is not suitable for most industrial applications because of the phosphate ion which has been incorporated in the final product and the resulting insolubles that are found in the reaction medium.
Another approach to producing stable cupric hydroxide is the ammonia-process cupric hydroxide, disclosed in U.S. Pat. Nos. 1,800,828; 1,867,357; 2,525,242; and 3,635,668. These materials are suitable for use as chemical intermediates, however, the individual particles are relatively course and exhibit varying degrees of fungicidal activity. The ammoniacal process also tends to produce cupric hydroxide of higher bulk density and lower surface area than the present method, hence lower reactivity per unit time compared to the present carbonate process cupric hydroxide.
Furthermore, inherent in an ammoniacal process is the problem of further processing the effluent. For example, in the so called "bug ponds" where waste water is treated, ammonia may be a biological poison, which damages the effectiveness of the bacteria in the pond. The ammoniacal process is further complicated in waste water treatment in that ammonia solubilizes the cupric hydroxide to a significant extent, thus further contaminating the waste water with copper and reducing the copper content of the product.
Historically unstable copper hydroxide has been prepared and used in the "Bordeaux" and "Burgundy" mixtures (named for the regions of France where the mixtures were first used as fungicides for grapes). The Bordeaux mixture is obtained by adding copper sulfate to a suspension of hydrated lime. The product is unstable copper hydroxide. The Burgundy mixture is obtained by adding sodium carbonate to a solution of copper sulfate to produce unstable basic copper carbonate (CuCO.sub.3 Cu(OH).sub.2).
In commonly owned U.S. Pat. No. 4,490,337 issued Dec. 25, 1984 a carbonate process is disclosed wherein an alkali metal carbonate is reacted with a soluble copper salt and the precipitate (copper carbonate) then treated with alkali hydroxide to convert a major portion of the precipitate to cupric hydroxide. The alkali metal hydroxide regenerates the alkali carbonate. The process is continued by alternately adding copper sulfate and alkali metal hydroxide. The alkali carbonate is an intermediate and alternating the additions may be repeated 15 to 20 times in this manner. In this process the carbonate radical must be preserved to provide the intermediate for the alternating copper reaction and regeneration. The present invention is much simpler in that it is a one step process and the liberation of carbon dioxide from the reaction medium is encouraged and desirable. Furthermore it has been found that the pH range is critical to produce stable cupric hydroxide composition.
The present method has a significant advantage over the related art in that neither ammonia, copper, nor phosphate are introduced into waste water. Another advantage is the presence of carbonate in the waste water, which is a practiced and accepted method of buffering industrial effluents. A feature of the present invention is absence of pollutants in the waste water stream. Another advantage of the present method is the production of much finer particles and much lower bulk density than presently available for similar materials. A further advantage is the use of aqueous dispersions of the carbonate process cupric hydroxide directly as foliage sprays without stickers (adhesive aids, such as starch).